This one just sort of happened when I used a paper towel to clean up after refilling my color print cartridge. I ran some water over it to get the blotches to spread and blend. After it dried I used a black sharpie marker to outline some shapes that I saw, kind of like a rorschach inkblot test.
I think this would work just as well with markers as the beginning source for the color blotches. I like the contrast of soft, blended colors and sharp, black outlines. I also like the movement that came from the water flowing down which was emphasized with the flying of the birds.